Familial Nasopharyngeal Carcinoma 6

72 T. C. Putti and K-B. Tan7.2Histopathological Typesof Nasopharyngeal Carcinoma NPCMost cases of NPC can broadly be classified asnonkeratinizing and keratinizing. The nonkeratinizinggroup can further be separated into undifferentiatedcarcinoma and differentiated carcinoma group.7.2.1Undifferentiated CarcinomaUndifferentiated carcinoma is the major histopathologicaltype of NPC, although the exact percentage indifferent populations varies. In endemic populations,undifferentiated carcinoma takes up between 47% and92% of all cases of NPC (Shanmugaratnam et al.1979; Tan and Putti 2005). In a major series on a western(non-endemic) population, this subtype of NPCconstituted only 44% of all NPCs (Al-Sarraf et al.1998). Undifferentiated carcinoma is characterizedmicroscopically by tumor cells with spindle-to-ovalvesicular or hyperchromatic nuclei bearing prominentnucleoli and which also feature scattered mitotic activity(Figs. 7.1–7.3). Variable numbers of intermixed lymphocytesand plasma cells are seen. There are twoclassically described patterns of growth: the “Regaud”pattern denotes a solid sheet-like tumor cell growthpattern, while the “Schmincke” pattern is typified by thepresence of apparently separated or loosely attachedtumor cells (sometimes described as a reticulatedpattern) with prominent intermixed lymphocytes(Glanzmann et al. 1976). This latter pattern exemplifiesthe previous terms for NPC: “lymphoepithelial carcinomaor lymphoepithelioma” (vide supra). Thesehistological patterns have no prognostic significance.7.2.2Differentiated Nonkeratinizing CarcinomaDifferentiated nonkeratinizing NPC is very similar histopathologicallyto undifferentiated carcinoma, exceptthat the tumor cells have a stratified or pavementedarrangement with cell borders being readily discernable(Chan et al. 2005) (Fig. 7.4). The tumor cells may have aplexiform arrangement, a growth pattern akin to that oftransitional cell carcinoma of the urinary tract. In seriesfrom Singapore, this tumor subtype constitutes between7% and 49% of cases of NPC (Shanmugaratnam et al.1979; Tan and Putti 2005). Nonkeratinizing NPC canrarely have a papillary architecture with tumor epitheliumcovering fibrovascular tissue cores (Fig. 7.5). Apartfrom histological similarities, differentiated nonkeratinizingNPC and undifferentiated NPC have comparableprognosis and their distinction is not thought to haveclinical significance (Chan et al. 2005).Fig. 7.1. Undifferentiatedcarcinoma featuringcohesive sheet of tumorcells with few intermixedlymphocytes (Hematoxylinand Eosin, original magnification×200)